According to Flood (2004), about 50 species of large animals, the
megafauna, including marsupials, reptiles and birds, went extinct in
Australia in the last 100,000 years, about 41 going extinct in the Late
Pleistocene. Most of the macropods that went extinct were browsers,
as was the Diprotodon.

There have been a number of causes proposed for the extinction of the
Australian Megafauna. On the other continents the megafauna went extinct
shortly after the arrival of humans, or shortly after humans developed
the technology necessary to hunt large animals, suggesting the humans may have
possibly hunted them to extinction. There is evidence for the hunting of
the megafauna, even the largest, the mammoths, in various parts of the
world. The name blitzkrieg has been coined for this suggested cause of
extinction of megafauna. In the Americas, the megafauna disappeared as
humans arrived in Alaska from Siberia, then spread all the way to the
southern tip of South America. The same happened in New Zealand and
Madagascar. In these places there are known kill sites, some where large
numbers of animals were killed. There are no known kill sites in
Australia.

In Australia there has been very little evidence found of large scale
hunting of megafauna. At
Cuddie
Springs, a shallow ephemeral lake near Carinda, in semiarid New
South Wales, the remains of megafauna animals have been found in
association with Aboriginal artefacts and evidence of Aboriginal
occupation, hearths and stone tools that still have traces of blood and
hair on them. Comparison of DNA from the bones of megafauna animals and the
traces on the stone artefacts shows that they were used to butcher Macropus titan
(a giant kangaroo)
and Diprotodon.
So at least at this place the Aborigines were eating megafauna animals.
It is usually accepted that the giant kangaroo, Macropus titan,
went extinct. There are those who believe that rather than becoming
extinct, they simply down-sized, evolving into the Eastern Grey
Kangaroo, Macropus giganteus, also known as the Great Grey
Kangaroo, the largest of which get about 2/3 of the size of
Macropus titan.

At Cuddie Springs, megafauna bones and artefacts occur in the same strata
in association with charcoal that provides secure dates. Artefacts are
found associated with bones of megafauna, as well as in earlier and
later levels. At 30,000 years ago the artefacts are associated with the
remains of Diprotodon and Genyornis.
Elsewhere in the world large stone points were associated with megafauna
hunting. These did not exist in Australia until thousands of years
later. At Cuddie Springs, where there is little doubt the people were
eating megafauna, the stone implements appear to be all of the type used
for processing carcases rather than hunting large animals. This has led
to the suggestion that the people may have been eating dead or dying animals
that had been trapped in the mud around the water's edge.

It has been suggested that a reason for the lack of evidence for the
hunting of large megafauna animals in Australia was the lack of the
large stone spear points used for that purpose elsewhere. If this was
the case, it doesn't necessarily mean the Aborigines simply didn't think
of it. They did use hardwood points that they fashioned with smaller
stone tools. Hardwood was widely available in Australia, but the sort of
stone necessary for large spear points was not, most of the stone used
by the Aborigines was stone types such as silcrete, very good for small
tools, not so good for large spear points. It was suggested that the
Aborigines probably hunted juvenile megafauna animals because of the
enforced limitation on their hunting equipment. This has been advanced
as at least a partial cause of the extinction, large animals usually
reproducing much more slowly than smaller ones, so being more
susceptible to the attrition of their populations. Juveniles would
provide less food than adults, so the hunters would have needed to kill
more individuals than if they hunted the adults.

At some locations, such as
Coral Bay in Western Australia, there is
evidence of harvesting of
Genyornis eggs. The shells showed evidence, in the form of
point-burning, as occurs when emu eggs were eaten and the shells peeled, some
fragments of shell dropping near the fire so that only a protruding point on a
piece of shell was burnt. If it was burnt in a bushfire the whole of the
shell would show signs of burning. But the evidence does not point to
large-scale plundering of the eggs. At some point, apparently a short
time after arriving in Australia, the Aborigines developed a method of
exploiting their food sources sustainably, such as they were known to
have practiced with emu eggs at the time of European contact, only
taking a few eggs from a clutch, always leaving enough to keep the emu
population at a sustainable level. They did the same when harvesting
root crops in other parts of the country, always leaving enough tubers
to provide another crop for the next harvesting season.
See Aboriginal
agriculture.

The Genyornis and emus had co-existed, usually nesting
in the same areas. Amino acid racemisation was used to date the shell of
the 2 birds. It was found by comparing the types of carbon in the
shells, both were herbivores, that while the Genyornis was
apparently a picky eater, the emu ate a much wider range of food. By
studying the emu egg shells before and after 50,000 years ago it was
found that emus were eating a very wide range of foods prior to the
extinction of Genyornis. After the extinction of the Genyornis the range of plants in the emu diet changed
radically, the variety of plant types being greatly reduced. After
45,000 years ago the emu diet changed substantially to a completely
different range of foods. The plants that Genyornis
depended on were mostly gone, so it is likely that hunting alone didn't
kill them off, though it would have been an added stress. The emu,
having such a wide range of food plants, simply adjusted its eating
habits to whatever was available.

The fossils of some Diprotodons have been found with
the remains of plant material about where their stomach would have been.
It showed that they were eating
saltbush, a
plant that thrives in the hot arid regions of central Australia. It has
been suggested that the demise of the Diprotodon and
other large herbivores may have been caused by a comparatively sudden
lack of suitable vegetation.

Using OSL dating it has been found that across Australia the
megafauna went extinct between about 51,000 and 40,000 years ago. More
precise dating of flowstones that cover the remains of megafauna at
sites such as
Naracoorte Caves, has
since narrowed down the time of extinction to 46,000 years ago. The most
recent megafauna fossils found have been 46,000 years old, from
Queensland and Western Australia, indicating the extinction occurred in
a relatively short period of time across the entire continent,
indicating that whatever the cause it was continent-wide in effect. As
the first Aborigines arrived at least 50,000 years ago, and more
probably 60,000 or more years ago, they must have coexisted with the
megafauna for a number of thousand of years. There has not been a single
site found that indicated the aborigines were decimating the megafauna
the way the Ica Age hunters did in other parts of the world. What
evidence there is of their interaction with them, such as the
Genyornis egg shell evidence, indicates that they had already
started to
harvest sustainably before the megafauna went extinct.

The episodes of active glaciers in the Snowy Mountains have been
dated. It indicates that there were 3 episodes of glaciers grinding
their way down the valleys, the first of which was during the time of
the megafauna, at 60,000 BP, then at 30,000 years and 20,000-19,000
years BP. The megafauna had survived the first of these glaciations
before or about the time the first of the humans arrived in Australia,
and they had died out long before the 3rd and most severe glaciation, at
the
glacial maximum. These glaciations did not match with times of
extinction, the megafauna mostly recovered after the first, and dry
periods since, but were extinct by the time of the second . It has been
suggested that while they had demonstrated that they could survive the
hard times, once human hunting, and habitat change, was added to the
mix, even though what evidence there is doesn't indicate large scale
overkills, it could have been enough to tip the balance against them.

By studying the record of climatic change at the
Naracoorte Fossil Site it was found that the megafauna had no
problem surviving either cold or dry periods, always bouncing back with
the return of more favourable conditions. All except the last one when
humans were also present in Australia. In spite of no evidence of large
scale overhunting it seems humans were again implicated in the demise of
the megafauna. Further confirmation that early Aborigines had indeed met
animals of the megafauna came with the discovery in a cave in Arnhem
Land of an ancient cave painting of a Palorchestes.
Mud-dauber wasps had built a nest over the pigment and had subsequently
been fossilised by the water running down the cave walls. These nests
have been dated, indirectly giving a minimum age for the painting of the
Palorchestes. At 40,000 BP, and possibly older, it is one
of the oldest known cave paintings in the world.

One feature of the changing Australian climate that may have affected
the megafauna more than glaciation and its accompanying dry conditions
was the progressive
aridification of the Australian continent that had been progressing
in stages since the Middle
Miocene. They had survived dry periods, but
the relentless spread of arid conditions, even before the arrival of
humans, may have been pushing the megafauna past their ability to adapt.
Drought-resistant, fire-tolerant/promoting or even requiring plants had been evolving and
spreading since the trend towards increasing
aridity began, with its associated increase in frequency and
severity of fire.

At the time the megafauna went extinct the vegetation of the
continent was changing on a large scale, and it occurred continent-wide.
It has been suggested that this was one time when the large size of the
herbivorous megafauna animals worked against them. They would have
required a large amount of food to maintain their bulk. As their food
sources became more scarce they would have found it difficult to find
enough to survive, eventually reaching the point where they were simply
dying of starvation, or being weakened so much that they became easy
prey for disease as well as their predators, human or animal. Once the
herbivores were gone the predators would follow. The reason for this
vegetation change is being researched. A likely contender for the main
cause is
firestick farming. Just at the time megafauna went extinct the rise
of the fire-promoting grass, such as spinifex, and trees, such as
eucalypts, increased in scale and extent. Just the sort of vegetation
promoted by firestick farming. This is believed to be responsible for
eliminating many fire sensitive species, including several types of
rainforest.

In Tasmania the megafauna survived about 5,000 years longer than on
the mainland, going extinct shortly after the arrival humans. It's
beginning to look like the introduction of widespread burning, rather
than direct hunting, may have been what proved too much for the megafauna. A
suggestion has been that a possible contributing factor may have been
that the first human arrivals perfected their sustainable way of life in
such a difficult environment only after the megafauna had gone extinct.

Aboriginal oral tradition tells some stories that may be memories of
the megafauna that have been passed down the generations. One such story
tells of an encounter with
giant
kangaroos (Flood, 2004). Another tells of a
giant
emu that had killed many people, could it have been Genyornis?
In this story, after the giant emu had been killed its feathers were all
split in 2 to make the normal sized emus of today (Isaacs, 2005). Could
this allude to the difference between the feathers of Genyornis
and the emu, emus feathers have a double shaft. The stories seem to be more about the danger
they posed and using fire as a defence against them than hunting them.
According to the story they lacked the weapons necessary to defend
themselves from giant kangaroos, so it would seem hunting megafauna may
have been more opportunistic kills than organised slaughter that kill
sites attest to on other continents. Even in New Zealand, a relatively
small island compared to the vast areas of North America and Eurasia
where megafauna were killed in great numbers at some kill sites, moa
kill sites have been found. The Aborigines encountered the megafauna
many thousands of years earlier than the Maoris first encountered the
moas. They would probably have been even
more afraid of the marsupial lion, Thylacoleo carnifex, if
they actually encountered these dangerous animals, as they probably did
when the first arrived on the continent.

In his Book, Australia's Mammal Extinctions, Dr Chris Johnson
covers in detail a wide range of theories for the extinction of
Australia's megafauna. Most of the Pleistocene fossil sites containing
megafauna have been found in southern Australia, such as at
Lake
Callabonna. Few fossil sites from the Pleistocene have been found in
northern Australia, so the whole of northern Australia can shed little
light on the life and death of the Australian megafauna. The best
Pleistocene sites from the north at the time of writing is the Mt Etna
caves of central Queensland (Hocknull, 2005). Johnson has suggested the
number of megafauna species that could have gone extinct may be grossly
underestimated, by as much as 20-30 %, because of the dearth of fossils
from the Pleistocene in the north of the continent, as many present day
animals are restricted to these northern areas, presumably during the
Pleistocene the area would have supported a large number of species not
present in the south.

Another problem connected with the small number of megafauna fossil
sites known is that many of the fossils are fragmentary and largely
incomplete. The lack of complete skeletons makes it difficult to infer
anything about the lifestyle or behaviour, or the type of environment it
lived in. One of the major problems is estimating body mass. Murray
(1991) studied the relationship between body length and body mass of
living marsupials, extrapolating the results to the size of the
megafauna. His results suggest Diprotodon optatum reached
a maximum body mass of not much more than 1,000 kg. Though this
indicated it was a large animal, it would be much smaller than many
megafauna animals from other parts of the world, much smaller than the
mammoths and ground sloths that weighed in at about 6,000 kg.

It has been found that many of the Australian megafauna had a
different build than their modern, smaller marsupial relatives, many
having a much stockier build, giving them a higher body mass to body
length relationship. Wroe et al. (2004b) carried out other measurements,
instead of using body mass to body length, his team used the
relationship between the thickness of leg bones and the body mass of
modern animals to try to get closer to the proportions of the megafauna.
These variables correlate closely because of the thickness an animal's
leg needs to be to support its weight. Using this method they arrived of
a body mass of about 2,700 kg for D. optatum. This puts
its size between that of a white rhino and a female Indian elephant.
This method was used by Helgen et al. to estimate the body mass of 11
extinct kangaroo species. In all cases it increased the body mass
compared with previously estimated masses. It is believed the actual
size of many other members of the megafauna are larger then the masses
previously applied to them (Johnson,2006).

Some believe the unproductive nature of Australian ecosystems led to
smaller sizes of the Australian megafauna compared to those from other,
more productive ecosystems on other continents (Flannery, 1994),
suggesting the herbivores of the megafauna evolved to cope with the
vegetation that survived on impoverished soils and low, erratic
rainfall, resulting in smaller maximum sizes. It has been shown on a
world scale there is a strong relationship between land mass area and the
maximum size of the largest vertebrates evolving on them (Burness et
al., 2001). According to these results, the maximum sizes of the
Australian megafauna were below that expected for the size of the
continent. This result was interpreted as a result of the low-energy
environments of Australia. The results were obtained using a mass of
about 1150 kg for D. optatum. Using Wroe's estimate of
2,700 kg for D. optatum, the sizes of Australia's
megafauna were actually greater than expected, showing that there was no
relationship between energy availability and the maximum size reached by
the animals of the area (Johnson, 2006)

A feature of the megafauna was the low numbers of large specialised
predators that have been found, but the most surprising feature was lack
of large scavengers. The large relatives of the Tasmanian devil that
lived in the Pleistocene were highly specialised, their jaws and teeth
being designed to crush the bones of large vertebrates. This is thought
by some (Johnson, 2006) to indicate that the possible role of large
reptiles in the Pleistocene, Megalania prisca in
particular, was as scavengers. Johnson (2006) suggests this could be a
result of the limitations on large carnivores caused by the low
productivity of the Australian environments. It is believed that as a
result of the productivity of the environment the herbivores were probably
widely spread out, having to cover large areas to find enough food, this
would lead to carcasses, either from natural death or carnivores, being
widely scattered, which in turn led to scavengers having to cover large
distances in search of carcasses. Reptiles are much better suited to a
lifestyle in which food is widely scattered and there would be long
periods between meals.

Size & Extinction

The extinctions in the Late Pleistocene were size related in
Australia and New Guinea. All species with greater masses than about 40
kg went extinct, as well as some smaller ones. The percentage of species
that went extinct in New Guinea was about 9 %, less than in Australia,
mostly because of the fewer large animals in New Guinea. Of the smaller
species going extinct, they were mostly larger than relatives that
survived. An example of these smaller animals that went extinct is
Borungaboodie hatcheri, a rat-kangaroo weighing about 10 kg. It
was the largest member of its family. Both the extinct species of
echidna in Australia were very large compared with the surviving modern
species, even though they were much smaller than the megafauna animals
that went extinct (Johnson, 2006).

The size selective nature of the
Pleistocene extinctions is
distinctive. Prior to the Pleistocene most of the megafauna lineages had
been increasing in size since the Miocene, indicating that large body
size wasn't being selected against prior to the Pleistocene. Extinctions
in the Holocene were species that were either of similar size or smaller
than their surviving relatives. The Nullarbor dwarf bettong (Bettongia
pusiia), a rat-kangaroo, is the only Australian mammal to
have gone extinct during the Holocene. It was a bit less than half the
size of living Bettongia species (McNamara, 1997).

Several Australian marsupial lineages have undergone what has been
called Late Pleistocene dwarfing, in such animals as devils, koalas and
kangaroos. This is also indicated in wombats, where Long et al. (2002)
suggest that Lasiorhinus angustidens, from the Late
Pleistocene, larger than living hairy-nosed wombats, may be ancestral
to them. A large number of Late Pleistocene species have now been
recognised as ancestral to populations of dwarfed modern species. An
example of this dwarfing is the giant kangaroo Macropus titan,
double the size of the largest living kangaroos, is now believed to be
ancestral to M. giganteus, the eastern grey kangaroo.
Similarly, Dendrolagus noibano, the late Pleistocene New
Guinea tree kangaroo, has been recognised as ancestral to the smaller
living tree kangaroo D. dorianus (Flannery et al., 1996).

Dwarfing reduced linear dimensions by up to 35 %, about half the body
mass. This effect was greatest in species that were close to the cutoff
mass for extinction. The eastern grey kangaroo is of similar size, or
slightly larger, than that of some extinct kangaroos. The Macropus
titan - M. giganteus lineage underwent the most
pronounced dwarfing. Kangaroo species of more then 10 kg that were far
enough below the cutoff size underwent a lesser amount of dwarfing, and
those less than about 10 kg appear to have not been dwarfed. The smaller
species had no problems with the cutoff size, the larger ones appear to
have had the best chance of surviving if they were close enough to the
cutoff to get small enough soon enough (Johnson, 2006).

Johnson has stated that for a theory of the Australian megafauna
extinctions of the late Pleistocene to be considered to be successful it
must explain the breadth and complexity of the
extinction, and the unifying feature of relatively large size that
characterises the extinction event.